The most badass book for growth hacking LinkedIn.
Hunt down all the Email addresses that you need with one click. Email Hunter for Chrome allows you to find a list of contacts behind the website that you are in and even more, it comes with an evaluation if they are still active. Convenient, isn't it?
Block "features" within LinkedIn with this free browser extension customizing LinkedIn the way you want. Add message templates/canned responses for easy compose, reply, invite messages.